Currently used to improve the color gamut of the small size of the display, the more promising application is using a quantum dot film (QD film) to excite the RG by the blue LED, wherein the width of the light line of the QD is about 30 nm, the narrow line width guarantees the true color of the backlight. In a backlight module containing a quantum dot film (also known as quantum dot backlight module), the blue LED is encapsulated on the light entrance side of the light guide plate, and the quantum dot film is usually placed on the light exit side of the light guide plate. When the quantum dot backlight module is in operation, the light source emitted by the blue LED through the lower polarizer containing the APCF below the liquid crystal cell structure will be re-through the quantum dot film, which leads to the secondary excitation problem of the quantum dots, so that the spectrum of the backlight changes. However, the panel manufacturer in the quantum dot film with color resistance design, usually need accurate spectral spectrum to carry out simulation calculations, and because the existence of secondary excitation makes the measured spectrum cannot be directly used for calculation, and the spectral variation due to the secondary excitation causes the relevant chromaticity index calculated by the backlight module to deviate from the final measured value.